Linear release of strontium ions from high borate glasses via lanthanide/alkali substitutions

The effect of increasing substitutions of La2O3:Na2O on the structure (11B MAS NMR) and properties, specifically strontium (Sr) ion release from five quaternary borate glass compositions (B2O3-SrO-Na2O-La2O3) was studied. To examine component ion release, samples were extracted under simulated physiological conditions at 37 °C for five extraction time points (24, 72, 168, 336 and 720 h). A linear release profile for strontium was provided by composition LB102 (70B2O3-20SrO-6Na2O-4La2O3) for up to 720 h. 11B MAS NMR was used to investigate the impact of La2O3:Na2O substitution on the boron structure and speciation. Substitutions appeared to have minor effects on borate speciation, with the only change being a decrease in the proportion of BO4 at maximum La2O3 loading (70B2O3-20SrO-10La2O3). These data further demonstrate the possible utility of high boron glasses as controllable degradable materials for the delivery of therapeutic metal ions, such as strontium.